There is considerable potential for the commercial development and military utilization of compact, portable, sealed TE CO.sub.2 lasers. The cost, ease of fabrication, reliability and overall system volume are important considerations in the commercial development of discharge excited gas lasers, particularly TE lasers utilizing CO.sub.2 as the main lasing material.
Discharge excited gas lasers are typically comprised of a housing which defines a gas tight laser discharge channel through which a lasing material is passed. In TE lasers, a pair of elongated main discharge electrodes are longitudinally disposed within the discharge channel in transversely spaced apart relation. Optical components are disposed at both ends of the channel. Laser action is achieved by exciting the lasing gas material with high energy, high voltage pulses applied across the electrodes by appropriate electrical circuitry.
In order to initiate and sustain proper laser action and avoid dissipation of energy in constrictive arcs between the electrodes, it is necessary to provide some means of producing a uniform glow discharge in the lasing gas mixture. The requirement is particularly acute at gas pressures above a few tens of torr to several atmospheres. Various arrangements have been conceived, certain of which are discussed hereinbelow, for conditioning and preionizing the lasing gas mixture and these typically play a significant role in the cost, ease of fabrication, reliability and overall system volume of TE lasers.
Several techniques have been developed for initiating and sustaining proper laser action. Among the simplest and most compact devices, ultraviolet (UV) radiation is used to condition the lasing gas mixture before and/or during the discharge. In most of these devices, the UV radiation is produced by a separate discharge, such as by trigger wires, or by separate UV producing arcs. Such arrangements are inherently complex, large and expensive.
A recently developed transversely excited atmospheric (TEA) discharge system relies on a type of corona discharge formation over the surface of a dielectric. The surface discharge produces an efficient ionizing UV radiation which results in the generation of a very homogeneous glow discharge. This system differs from the above mentioned systems in that no additional UV source is present and the excitation rate is very fast. Further, this system operates with a variety of gas mixtures without the need of a dopant and the highly homogeneous character of the discharge results in high power outputs per unit volume and large gains.
Notwithstanding the foregoing, the highly stressed dielectric may lead to problems, particularly at high repetition rates. Further, it is difficult to arrange for high speed transverse gas flow, which is essential for high repetition rate operation, when employing this type of preionization. A very rapid discharge circuit (pulse risetimes in the order of 20-50 ns) places still further restrictions on the construction of a laser of this type. For example, difficulties may arise if the laser discharge module has to be located remotely from the power supply and energy storage capacitors. This configuration tends to increase the inductance of the discharge circuit and thus may prevent operation of the laser. Still further, thyratron switching may not be possible due to the increased circuit inductance.